Zircon grain shape parameters from ignimbrites of the Central Anatolian Volcanic Province (CAVP) with implications for petrogenetic processes

Abstract

Zircon morphology parameters reflect the physicochemical conditions during crystallization and can be modified by different processes. Zircon populations from Miocene-Pliocene ignimbrites of the Central Anatolian Volcanic Province (CAVP) were studied to reveal relations between the external morphology of zircons and petrogenetic processes. Descriptive grain shape parameters (e.g., minor and major axes, area, perimeter, aspect ratio, roundness, and circularity) were automatically measured from transmitted light images of zircons by a graphical application called AnalyZr. Principal component and cluster analysis were used to determine potential shape descriptors (perimeter, major and minor axis length, and maximum and minimum Feret) for characterizing grains from a particular rock. Accordingly, zircons from ignimbrites display morphological variations, which can be attributed to a specific magmatic process. Zircon isotopic compositions from previous studies indicate that ignimbrites are derived from mantle sources, but due to the distinct contributions of crustal components and periodic mafic recharge, isotopic heterogeneity occurs in the genesis of the ignimbrites. Furthermore, the typological evolution of zircons has already revealed that even a small decrease in saturation and crystallization temperature can significantly alter the external morphology of zircons. The clear imprint of hybridization in the zircon morphology of CAVP ignimbrites might provide information about the development of zircon within silicic melts. This study offers new insight into the integration of data on shape and isotope variations in zircon populations that can be traced back to the magmatic controls on zircon crystal growth.